The present invention relates to a method for forming an inter-layer insulation film. More specifically, the present invention relates to a method for forming an organic/inorganic hybrid insulation film having a function of preventing Cu ions from diffusing by means of a plasma CVD method.
In recent years, a Cu wiring technology using Cu as a wiring material has been introduced in order to deal with VLSI (Very large Scale Integration) operated at an increasingly higher speed. However, the technology includes a problem that Cu ions are diffused in an inter-layer insulation film due to an electric field or heat, which causes a breakdown voltage of the inter-layer insulation film to deteriorate in a long-term use. When the breakdown voltage of the inter-layer insulation film is thus deteriorated, an insulation failure thereby generated leads to an operation failure of the VLSI.
Therefore, the VLSI including the Cu wiring has so far employed a Cu diffusion preventing film for preventing the diffusion of the Cu ions. A problem in using such a film is that any of SiN, SiON, SiC or SiCO, which are known as a material of an insulation film designed to be used as the Cu diffusion preventing film, has a high dielectric constant of ≧4. Therefore, when a film having a low dielectric constant of approximately 2 to 3 is used as the inter-layer insulation film as a solution, the dielectric constant of the conventional Cu diffusion preventing film having such a high dielectric constant exerts a dominant contribution in a multi-layer wiring structure. To be more specific, when the dielectric constant of the inter-layer insulation film is reduced, an effect resulting from the reduced dielectric constant is counterbalanced by the conventional Cu diffusion preventing film having a high dielectric constant. Therefore, an effective dielectric constant in the entire multi-layer wiring is not reduced to a satisfactory level.
In the presence of the problem, it is presently demanded that the dielectric constant of the Cu diffusion preventing film be reduced or a Cu diffusion preventing function be provided to the inter-layer insulation film having a low dielectric constant.
As a conventional technology for reducing the dielectric constant of the Cu diffusion preventing film, a method for forming a SiCN film by means of a plasma CVD (Chemical Vapor Deposition) using trimethylvinylsilane is reported. The dielectric constant achieved by the method is, however, approximately 4, which is not low enough. There is another report of a method for forming the low-dielectric-constant film having the Cu diffusion preventing function by means of the plasma CVD employing divinylsiloxane bisbenzocyclobutene (as an example of which, see Japanese Unexamined Patent Publication No. 2000-12532). Referring to the report, it is shown that a film having the dielectric constant of approximately 2.7 is formed.